This invention concerns a single phase bipolar electromagnetic stepping motor for timepiece use being capable of rotation in both senses and comprising a stator formed of a soft ferromagnetic material and a rotor constituted by a magnet having at least one pair of poles.
Electromagnetic single phase stepping motors with two rotation senses are known and to overcome difficulties which they may present the applicant has proposed a new solution in U.S. patent application No. 122,955 and which claims the fact that the moment of inertia, the volume and the number of pole pairs of the rotor are combined in order to satisfy a certain mathematical relationship and that the said rotor is driven in a rotation sense opposed to the preferred sense when the motor winding receives double pulses of alternate polarity comprised of a first pulse of which the polarity causes the rotor to turn through an angle less than one step in the preferred sense, the said first pulse being immediately followed by a secod pulse of which the polarity is opposed to the first, the said second pulse causing the rotor to turn through an entire step in the sense opposed to the preferred sense.
The invention which has just been mentioned is applied essentially to timepieces having only an hours hand and a minutes hand, that is to say to a motor of which the rotor advances only through one step each minute. Effectively the weight and increase in complexity as provided for this rotor, taking into account the necessity to assure a correct operation in both senses, must be compensated for by an increase in current consumption even during the normal operation of the watch. It follows that this type of motor is less suitable for a watch provided with a seconds hand where the rotor is caused to step one increment each second. The mentioned invention further requires that the motor winding be fed by a type of pulses which are composite and alternative thus rendering more difficult the feeding arrangement.
It is the purpose of the present invention to provide a stepping motor with operation in both senses of rotation, and which overcomes the difficulties cited, in which the consumption does not exceed that of an optimal motor having one sense of rotation only and in which the motor winding is fed by a simple type of alternating pulse.
It is another purpose of this invention to assure a more certain turning (or couple) in reverse rotation, such not being obtained with the systems of the prior art, and to avoid the necessity for a counter electromotive force detector, as provided in certain of these systems.
These purposes are obtained thanks to the claimed means.